This invention relates generally to thermoelectrically-powered wrist watches, and more particularly to a wrist watch of this type whose construction is such as to minimize shunt heat losses whereby the thermoelectric generator housed therein operates at high efficiency.
It is known to power analog or digital solid state wrist watches by means of a thermoelectric generator which operates on the Seebeck effect to develop a voltage due to differences in temperature between two junctions of dissimilar metals in the same circuit. In thermoelectrically powered wrist watches of this type, the components of the watch movement are supported on a metal carrier that is held within the watch casing with the major portion of the carrier in close proximity to the metal back of the casing.
The thermoelectric generator is placed within the casing with its hot pole in contact with the casing back. This back, which is of good thermal conductivity, is pressed against the wrist of the wearer to be heated thereby, the cold pole of the generator being in contact with the relatively cool carrier to provide the necessary heat differential for developing the voltage.
Because of the close proximity of the metal carrier to the heated casing back, a transfer of thermal energy takes place therebetween which tends to equalize the temperature. This effectively acts as a thermal shunt or bridge across the thermal generator. The resultant heat loss reduces the efficiency of the generator.
While an undesirable heat transfer can, to some degree, be reduced by filling the space between the metal casing back and the metal carrier for the movement with thermal insulation, such insulation does not satisfactorily solve the problem. A more effective practical solution is to provide a relatively large spacing between the casing back and the metal carrier, but this necessarily results in a casing of greater thickness or height and hence in a watch whose bulky appearance leaves much to be desired in aesthetic or ornamental terms.